The present invention pertains to the purification of anhydrous aluminum chloride.
Aluminum chloride is used as a catalyst in organic chemistry and it can be used to prepare aluminum. Two groups of industrial processes are available for its manufacture; the reaction of gaseous chlorine with molten aluminum and the carbochlorination of aluminum. The reaction of aluminum, chlorine and a carbon-containing material, which can be coke or carbon monoxide, is used in the second group. However, depending on the nature and the origin of the carbon, organochlorine compounds, which can be aromatic, or their condensation products are found in the aluminum chloride obtained, in addition to certain metal chlorides. It is often necessary to use pure aluminum chloride in catalysis or in cosmetic preparations and the presence or organochlorine compounds is highly troublesome and also deleterious.
Regardless of the origin of the aluminum chloride, the problem of purification arises if it contains organochlorine compounds.
The removal of organic impurities present in aluminum chloride has been described in several publications.
The purification of aluminum chloride containing hexachlorobenzene by passing the mixture of AlCl.sub.3 and C.sub.6 Cl.sub.6 over aluminum at 600.degree. C. is described in Japanese Patent Application No. 31,452/66 of Mar. 29, 1966. The C.sub.6 Cl.sub.6 is completely destroyed, and carbon is precipitated on the surface of the aluminum. The aluminum is generated by heating at 600.degree. C. in the presence of air to oxidize the carbon. A similar process, in which iron having a temperature of 805.degree. C. is used, or AlCl.sub.3 containing C.sub.6 Cl.sub.6 is passed into a zinc bath at 700.degree. C., is disclosed in Japanese Patent Application No. 31,451/66 of Mar. 29, 1966.
It is explained in U.S. Pat. No. 4,541,907 that by passing AlCl.sub.3 containing organochlorine impurities, which are essentially represented by C.sub.6 Cl.sub.6, over aluminum and carbon in a fluidized bed, an aluminum chloride free of chlorinated products is obtained. These processes have the disadvantage of involving the use of elevated temperatures.
It is also possible to use conventional separation processes based on the differences between the sublimation temperatures and/or the boiling points or between the adsorptions on various supports. However, these processes have the disadvantage that the aluminum chloride is incompletely purified and that they do not lead to destruction of the impurities. Products rich in organochlorine compounds are obtained which cannot be treated.